The present invention relates to an optically variable security element for securing valuable articles, a method for manufacturing such a security element and a data carrier that is equipped accordingly.
For protection, data carriers, such as value or identification documents, or other valuable articles, such as branded articles, are often provided with security elements that permit the authenticity of the data carriers to be verified, and that simultaneously serve as protection against unauthorized reproduction. Security elements having viewing-angle-dependent effects play a special role in safeguarding authenticity, as these cannot be reproduced even with the most modern copiers. Here, the security elements are furnished with optically variable elements that, from different viewing angles, convey to the viewer a different image impression and, depending on the viewing angle, display for example another color or brightness impression and/or another graphic motif.
In this context, optically variable security elements are known that display different movement or tilt effects when the security element is tilted, such as moving bars, moving pictorial depictions, pump effects or three-dimensional depictions. To implement the optically variable appearances, in the background art, different techniques are used that typically permit some of said movement effects to be realized particularly well and others less well.
For a three-dimensional depiction, typically, different views are provided for the left and right eye of the viewer in so-called stereographic methods, from which views a three-dimensional impression is then created. Here, a viewer sees an ostensibly identical image point with the left and right eye at different locations on the security element and then unconsciously calculates depth information via the corresponding parallaxes.
From document DE 10 2010 049 831 A1 is known, for example, an optically variable surface pattern that provides corresponding spatial views not only viewed from right and left, but also from top and bottom. Such a surface pattern offers a vertical as well as a horizontal parallax. While this has the advantage that such a surface pattern can be rotated arbitrarily in its plane without the spatial impression being lost, it simultaneously has the disadvantage that it requires many different views to be nested within one another, such that each view can occupy only a small areal fraction. The depictions are thus often relatively faint and in some cases are easily perceptible only when illuminated with a strong point light source.
Another approach to producing three-dimensional depictions having a horizontal and a vertical parallax is known from document DE 10 2010 048 262 A1. There, a depiction element is formed from individual “light spots” that are created in the focus of, for example, a concave or convex mirror or a metalized Fresnel lens. Such a depiction can be very bright and luminous provided that the surface regions associated with the individual light spots do not overlap too strongly, since in that case a nesting is likewise required and the brightness and luminance decreases. Luminous depictions can thus be produced only for images composed of relatively few light spots, which, however, results in a dotted and often sparsely detailed appearance.
A further possibility for producing depictions having a three-dimensional depth effect are offered by moiré magnification arrangements based on microlenses and microimages, as are known, for example, from document WO 2005/052650 A2. Here, a periodic depiction in the form of many small microimages is magnified by means of a grid composed of microlenses of similar but not exactly identical period. In this way, depending on the choice of the line screens, a depiction that apparently lies in front of or behind the actual surface pattern can result, or a so-called orthoparallactic movement can be produced. Disadvantageous in such moiré magnification arrangements, however, is the comparatively complex manufacture with two embossing steps for the microlenses and for embossed microimages, as well as the fact that only periodic depictions can be displayed.
Finally, it is known, for example from WO 2014/108303 A1, to align magnetically aligned reflective pigments, with magnets shaped accordingly, in such a way that bright, especially ring-shaped depictions result that likewise can comprise a certain depth effect. Such depictions are very bright and easily visible, but the required magnetic inks are comparatively expensive and the variety of effects and the resolution is limited by the availability of corresponding magnets.